1. Field of the Invention
The present invention relates to a method for manufacturing thin film transistor to be used for liquid crystal display devices, luminescent display devices and LSIs. In more detail, the present invention relates to a method for manufacturing a thin film transistor by forming a thin film constituting the thin film transistor using a liquid material.
2. Description of the Art
A thin film transistor is usually composed of thin films, such as semiconductor films, insulation films and conductive films. When these thin films are categorized depending on their functions, the insulation film includes gate insulation films and interlayer insulation films, and the conductive film is used for gate electrodes, source/drain electrodes, pixel electrodes and wiring lines. These thin films have been mainly deposited by a CVD (Chemical Vapor Deposition) method and a sputtering method.
Silicon films, such as amorphous silicon films, and poly-silicone films have been mainly used for the semiconductor films. The silicon films have been usually formed by a thermal CVD method, a plasma CVD method or a photo-CVD method using monosilane gas or disilane gas. The thermal CVD method has been generally used for depositing the poly-silicon film (J. Vac. Sci. Technology, vol. 14, p1082 (1977)), while the plasma CVD method has been widely used for depositing the amorphous silicon (Solid State Com., vol. 17, p1193 (1975)).
However, the silicon film formed by the CVD method have involved some problems which need to be improved in the manufacturing process: (1) manufacturing yield is low due to contamination of the manufacturing apparatus and generation of foreign substances, since silicon particles appear in the gas phase to be used for the gas phase reaction, (2) a silicon film with a uniform thickness can not be deposited on a substrate having a rough surface, since a gaseous starting material is used, (3) a step for heating the substrate is required, and productivity is low due to a slow deposition rate of the film, and (4) a complicated and expensive microwave generator and an evacuation apparatus are necessary in the plasma CVD method.
Handling of highly reactive gaseous silicon hydride to be used as a starting material is difficult, in addition to requiring an air-tight evacuation apparatus as well as a pollutant elimination apparatus for the treatment of exhaust gases. Not only is such a large scale facility itself expensive, but also a large amount of energy is consumed in the vacuum system and plasma system, rendering the product a high manufacturing cost.
A method for coating liquid silicon hydride that is free from the vacuum system has been proposed in recent years. Japanese Unexamined Patent Application Publication No. 1-29661 discloses a method for forming a silicon thin film by allowing a gaseous material to be liquefied and absorbed on a chilled substrate as a liquid, followed by allowing the substrate to react with chemically active atomic hydrogen. However, the method also involves a problem that a complicated apparatus is required for continuously evaporating and liquefying silicon hydride, and control of the film thickness is difficult.
While Japanese Unexamined Patent Application Publication No. 7-267621 discloses a method for coating the substrate with low molecular weight liquid silicon hydride, on the other hand, handling of this complex system is so troublesome that it is difficult to obtain a uniform film thickness when applied to a large area substrate.
While an example of a solid silicon hydride polymer has been reported in UK Patent GB-2077710A, it is impossible to form a film by coating since the compound is insoluble in solvents.
The silicon semiconductor film as described above is usually used as a positive or negative type semiconductor by doping Group III elements or Group V elements in the periodic table. These elements are usually doped by heat diffusion or an ion-injection method after forming the silicon film. Since the heat diffusion method is in principle a high-temperature process (requiring a temperature as high as more than 800xc2x0 C.), the material available as the substrate is limited. In particular, a glass substrate used for liquid crystal devices is not suitable for the high temperature process. Although the ion-injection method has a feature that impurity distribution toward the depth of the silicon film can be controlled, on the other hand, it is a problem that an evacuation apparatus is necessary besides the apparatus is large in size and heavy as well as expansive.
A dope silicon film in which impurities are doped has been also formed by the CVD method that is used for forming conventional non-dope silicon films. However, this method for forming the dope silicon film involves all the features and problems in the CVD method.
The hot CVD method and plasma CVD method as used in forming the silicon film are also used in forming insulation films such as a gate insulation film and an interlayer insulation film to be used in the thin film transistor. While the insulation film and organic insulation film formed of SOG are frequently used for the purpose of planarization, they are seldom used alone but are used together with the film formed by the CVD method.
The sputtering method is widely used for forming a gate electrode to be used for the thin film transistor, conductive films for the electrode such as source/drain electrodes, a conductive film for wiring lines, and a transparent conductive film to be used for pixel electrodes.
The CVD method involves the following four features, which are the same as those in forming the silicon film as an insulation film: (1) manufacturing yield is low due to contamination of the manufacturing apparatus and generation of foreign substances, since silicon particles appear in the gas phase to be used for the gas phase reaction, (2) a silicon film with a uniform thickness can not be deposited on a substrate having a rough surface, since a gaseous starting material is used, (3) a step for heating the substrate is required, and productivity is low due to a slow deposition rate of the film, and (4) a complicated and expensive microwave generator and an evacuation apparatus are necessary in the plasma CVD method.
An evacuation apparatus, in addition to a vacuum pump as well as a target material, a sputtering power source and a substrate heating apparatus, are required for the sputtering method to be utilized in forming the conductive film which mainly includes a metal film and the transparent conductive film. Although a toxic and combustible gas is seldom used in the sputtering method as compared with the CVD method, the film is deposited not only on the substrate as a film deposition object, but also on the inner wall of the chamber in which the substrate is placed. Peeled pieces of the deposition material from the inner wall serve as foreign substances during the film deposition process to result in decreased manufacturing yield of the product as in the CVD method. It is the common drawbacks of the sputtering method with the CVD method that the film thickness is uneven at the rough portions on the surface of the substrate, productivity is low, and the facilities become large scale and expensive because an evacuation apparatus is required.
Accordingly, the method for forming the thin film by the conventional CVD method and sputtering method have involved the common problems of low productivity, high incidence of film defects and low yield, uneven film thickness at the rough surface portions, and breakage of wiring patterns at the steps. These problems also cause increased manufacturing cost of the thin film transistor. These problems in the CVD method and sputtering method arise from intrinsic features of the film deposition method such as use of the evacuation apparatus, need of heating of the substrate, requirement of a power source for plasma generation, and film deposition on unnecessary portions such as the inner wall of the apparatus other than the substrate. These intrinsic features arise other problems that the large scale apparatus leads to a high facility cost, and the running cost of the apparatus is also high.
In the conventional method for injecting impurities into the silicon film, the CVD method involves the same problem as described above, while the ion injection method involves the problems of expansive apparatus and high running cost. These problems result in high cost of the thin film transistor manufactured by the conventional method.
The present invention proposes a method for manufacturing a thin film transistor by a novel method essentially different from the conventional film deposition method. The object of the present invention is to solve the intrinsic problems in the conventional film deposition method, enabling the thin film to be formed with high productivity, small incidence of film defects, high manufacturing yield, no breakage of wiring lines at the steps, and low manufacturing cost using a small size and cheap apparatus, thereby manufacturing the thin film transistor with an extremely lower cost than the conventional ones.
All or a part of the thin films such as the silicon film, insulation film and conductive film constituting the thin film transistor are formed using a liquid material in the present invention for solving the foregoing problems. Introduction of impurities and control of the amount of the impurities required for manufacturing the thin film transistor are realized by forming the thin film of silicon using liquid materials. The method for forming the thin film using the liquid materials mainly comprises the steps of forming a coating film by coating a substrate with the liquid material, and forming a desired thin film by heat-treating the coating film.
In a first aspect, the present invention provides a method for manufacturing a thin film transistor comprising each thin film of a silicon film in which the impurity concentration has been controlled, an insulation film and a conductive film, the silicon film in which the impurity concentration has been controlled comprising a non-dope silicon film and a dope silicon film, wherein the non-dope silicon film is formed by the steps comprising forming a coating film by coating a substrate with a liquid material containing silicon atoms, and heat-treating the coating film for converting it into the non-dope silicon film, and wherein the dope silicon film is formed by the steps comprising forming a coating film by coating the substrate with a liquid material containing the silicon atoms and boron or phosphorous, and heat-treating the coating film for converting it into the dope silicon film.
Preferably, the non-dope silicon film forms a channel region and the dope silicon film forms source/drain regions. The dope silicon film also forms electrodes and wiring lines.
In a second aspect, the present invention provides a method for manufacturing a thin film transistor comprising each thin film of a silicon film in which the concentration of impurities has been controlled, an insulation film and a conductive film, for obtaining the silicon film in which the concentration of the impurities including the concentration of desired impurities has been controlled, comprising the steps of forming a coating film by coating the substrate with a mixed solution of a liquid material containing silicon atoms and a liquid material containing the silicon atoms and impurities, and heat-treating the coating film to convert it into the silicon film in which the concentration of the impurities has been controlled.
The silicon film in which the concentration of the impurities including the concentration of desired impurities has been controlled may form a channel region.
In a third aspect, the present invention provides a method for manufacturing a thin film transistor comprising each thin film of a silicon film in which the concentration of impurities has been controlled, an insulation film and a conductive film, the silicon film in which the concentration of the impurities has been controlled comprising a laminated film of a non-dope silicon film and dope silicon film, wherein the non-dope silicon film is formed by the steps of forming a coating film by coating the substrate with a liquid material containing silicon atoms, and heat-treating the coating film for converting it into the non-dope silicon film, and wherein the dope silicon film is formed by the steps comprising forming a coating film by coating the substrate with a liquid material containing the silicon atoms and impurities, and heat-treating the coating film for converting it into the dope silicon film.
Preferably, the silicon film comprising a laminated film of the non-dope silicon film and dope silicon film forms a channel region.
In a fourth aspect, the present invention provides a method for manufacturing a thin film transistor comprising each thin film of a silicon film in which the concentration of impurities has been controlled, an insulation film and a conductive film, comprising the steps of: forming a coating film by coating a liquid material containing silicon atoms or a liquid material containing silicon atoms and impurities on an insulation substrate or an insulation film; heat treating the coating film to convert it into the silicon film in which the concentration of the impurities has been controlled; forming an islet region that serves as a source, drain and channel by patterning the silicon film; forming a gate insulation film; forming a gate electrode; exposing the silicon film that serves as source/drain regions by removing the gate insulation film on the source/drain regions using the gate electrode as a mask; forming a coating film by coating the liquid material containing the silicon atoms and impurities on the exposed source/drain regions; applying a first heat-treatment for forming a dope silicon film by heat-treating the coating film; applying a second heat-treatment for diffusing the impurities in the dope silicon film into the silicon film as a lower layer; forming a pattern overlapping a part of the source/drain regions by patterning the dope silicon film; forming an interlayer insulation film; opening contact holes on the interlayer insulation film; and forming electrodes.
In a fifth aspect, the present invention provides a method for manufacturing a thin film transistor comprising each thin film of a silicon film in which the concentration of impurities has been controlled, an insulation film and a conductive film, comprising the steps of: forming a coating film by coating a liquid material containing silicon atoms and impurities on an insulation substrate or insulation film; forming source/drain regions by heat-treating the coating film to convert it into the dope silicon film; forming a coating film by coating a liquid material containing silicon atoms or a liquid material containing silicon atoms and impurities on the substrate; heat-treating the coating film for converting it into the silicon film in which the concentration of the impurities has been controlled; forming an islet region containing the channel region for connecting to the source/drain regions by patterning the silicon film in which the concentration of the impurities has been controlled; forming a gate insulation film; forming a gate electrode; forming an interlayer insulation film; opening contact holes on the interlayer insulation film; and forming electrodes.
In a sixth aspect, the present invention provides a method for manufacturing a thin film transistor comprising each thin film of a silicon film in which the concentration of impurities has been controlled, an insulation film and a conductive film, comprising the steps of: forming a gate electrode on the insulation substrate or insulation film; forming a gate insulation film; forming a coating film by coating a liquid material containing silicon atoms or a liquid material containing silicon atoms and impurities on the substrate; heat-treating the coating film for converting it into the silicon film in which the concentration of the impurities has been controlled; forming a coating film by coating a liquid material containing silicon atoms and impurities; forming source/drain regions as silicon films doped with impurities by heat-treating the coating film; and forming electrodes.
In accordance with the first to sixth aspects, the present invention provides a method for manufacturing a thin film transistor, wherein the heat-treatment step comprising forming the coating film by coating the liquid material on the substrate, followed by forming the silicon film in which the concentration of the impurities has been controlled by heat treating the coating film, comprises a first heat-treatment step for removing a solvent from the coating film, and a second heat-treatment step for forming the silicon film in which the concentration of the impurities has been controlled.
In accordance with the first to sixth, aspects the present invention provides a method for manufacturing a thin film transistor, wherein the heat-treatment step comprising forming the coating film by coating the liquid material on the substrate, followed by forming the silicon film in which the concentration of the impurities has been controlled by heat treating the coating film, comprises a first heat-treatment step for removing a solvent from the coating film, a second heat-treatment step for forming the silicon film in which the concentration of the impurities has been controlled, and a third heat-treatment step for crystallizing the silicon film in which the concentration of the impurities has been controlled.
In the present invention so configured as described above, the first heat-treatment step preferably comprises a drying step for removing the solvent, and a heat-decomposition and/or photo-decomposition step in the coating film. The photo-decomposition step preferably comprises irradiating a light with a wavelength of more than 170 nm and less than 380 nm to the coating film. In a preferable embodiment, the second and third heat-treatment steps comprises a heat-treatment by lamp annealing or laser annealing. In an another preferable embodiment, the first, second and third heat-treatment steps comprises treating the silicon film in an atmosphere in which the oxygen concentration is controlled so that the concentration of oxygen contained in the silicon film, which is formed via the heat-treatment steps and in which the concentration of the impurities has been controlled, is 100 ppm or less.
The present invention so configured as described above provides a method for manufacturing a thin film transistor comprising each film of a silicon film in which the concentration of the impurities has been controlled, an insulation film and a conductive film, wherein the step for forming the insulation film comprises coating polysilazane on the substrate, and heat-treating the coated polysilazane for converting it into a SiO2 film.
The present invention so configured as described above provides a method for manufacturing a thin film transistor comprising each film of a silicon film in which the concentration of the impurities has been controlled, an insulation film and a conductive film, wherein the step for forming the conductive film comprises forming a coating film by coating a liquid material containing a metal on the substrate, heat-treating the coating film for converting it into a conductive film, and patterning the conductive film.
The present invention so configured as described above provides a method for manufacturing a thin film transistor, wherein the step for forming the conductive film comprises forming a conductive film on the substrate by a plating method, and patterning the conductive film.
The present invention so configured as described above provides a method for manufacturing a thin film transistor, wherein the step for forming the conductive film comprises forming a coating film by coating an organic compound containing indium and tin on the substrate, and heat-treating the coating film for converting it into an ITO film.
The present invention so configured as described above provides a method for manufacturing a thin film transistor, wherein the liquid material for forming the silicon film, in which the concentration of the impurities has been controlled, is a solution containing a silicon compound comprising a cyclic group represented by a general formula of SinXm (wherein n denotes an integer of 5 or more, m denotes an integer of n, 2nxe2x88x922 or 2n, and X represents a hydrogen atom and/or a halogen atom). Preferably, n is 5 or more and 20 or less in the silicon compound comprising a cyclic group represented by a general formula of SinXm.
The present invention also provides a method for manufacturing a thin film transistor, wherein the liquid material for forming the silicon film in which the concentration of the impurities has been controlled is a solution containing a silicon compound represented by a general formula of SiaXbYc (wherein X represent a hydrogen atom and/or a halogen atom, Y represents a boron atom or a phosphorous atom, a denotes an integer of 3 or more, b denotes an integer of a or more and (2a+c+2) or less, and c denotes an integer of 1 or more and a or less). Preferably, (a+c) is 5 or more and 20 or less in the silicon compound described above.
In the present invention so configured as described above, the solution containing the silicon compound preferably has a concentration of 1 to 80% by weight. It is preferable that the solution has a viscosity of 1 to 100 mPa.s. It is also preferable that the solution contains a solvent having a vapor pressure of 0.001 to 100 mmHg. The solvent is preferably a hydrocarbon based solvent.
The present invention also provides a method for forming a thin film transistor comprising each film of a silicon film in which the concentration of impurities has been controlled, an insulation film and a conductive film, wherein all the thin films or most of the thin films of each thin film are formed by a method using liquid materials, and the thin films are formed by a method not using an evacuation apparatus.
The present invention also provides a method for forming a thin film transistor comprising each film of a silicon film in which the concentration of impurities has been controlled, an insulation film and a conductive film, wherein the thin film transistor comprises a transparent conductive film, all the thin films or most of the thin films of each thin film are formed by a method using liquid materials, and the thin films are formed by a method not using an evacuation apparatus.
The present invention so configured as described above provides a method for forming a thin film transistor, wherein the method for forming a coating film by coating the liquid material on the substrate comprises any one of a roll-coat method, curtain coat method, dip-coat method, spray method or ink-jet method, or a combined method of any one of the foregoing methods and a spin-coat method in the method for forming each thin film with the liquid materials.